Method for producing epoxides by oxidising olefins

ABSTRACT

The invention relates to a new method for producing epoxides by oxidizing olefins in a homogeneous gas phase reaction, wherein ozone and NO 2  and/or NO are reacted with the desired olefin under mild reaction conditions and without a catalyst. The inventive method can be carried out as a continuous, one-step method in a reactor according to FIG.  1,  and requires very little technical input. Monoolefins having 2 to 16 carbon atoms and diolefins having 4 to 16 carbon atoms can be epoxidized.

DESCRIPTION

[0001] The invention relates to a new method of producing epoxides viaoxidation of olefins in a homogeneous gas-phase reaction by reactingozone and NO₂ and/or NO the desired olefin under mild reactionconditions without using a catalyst. The method of the invention can becarried out as a continuous one-step method in a reactor according toFIG. 1, and requires very little technical input. Monoolefins having 2to 16 carbon atoms and diolefins having 4 to 16 carbon atoms can beepoxidized.

[0002] Epoxides are important intermediates in the chemical industry andare mainly used in the production of olefin glycols or di-, poly- oroligomers thereof which mostly are processed further to formpolyurethanes. In particular, propylene oxide and ethylene oxide eachare required in amounts of about 5 million tons per year.

[0003] Epoxides can be produced from olefins by the chlorohydrinprocess, by indirect oxidation processes using -peroxide reagents, andby catalytic or non-catalytic direct oxidation processes. The oxidationscan be carried out in liquid phase or in gaseous phase. Oxidations inliquid phase, which can be carried out either as homogeneous orheterogeneous oxidations, are associated with difficult separationprocesses and, complicated technologies. Direct olefin oxidationprocesses in the gaseous involve relatively long residence times andfrequently furnish excessively low conversion and/or excessively lowselectivity with respect to the epoxide.

[0004] Thus, for example, DE 197 54 303A1 describes a method ofproducing propylene oxide from propylene in a homogeneous gas-phasereaction. While this method has a selectivity with respect to propyleneoxide of >60%, the propylene conversion is relatively low, being 13% and15%, respectively. In addition, the method is technically complex andcostly because the reactor's interior according to this invention islined with an inert material, particularly with noble metals.

[0005] It was the object of the present invention to provide a method ofproducing epoxides by oxidizing olefins, which method requires lowtechnical input, is favorable in cost, and ensures both high selectivitywith respect to the epoxide produced and high conversion of the olefinemployed.

[0006] It was found that epoxides can be produced via oxidation ofolefins in a homogeneous, continuous gas-phase process with good yieldsand good selectivities with respect to the epoxide produced, by mixingozone and NO₂ and/or NO, optionally using a carrier gas, passing theresultant gas mixture into a conventional flow reactor, and reacting thecorresponding olefin fed with the carrier gas under mild reactionconditions. According to the invention, a pressure of not more than0.1-1000 mbar, preferably 1-500 mbar, and more preferably 1-200 mbar, isrequired. The temperature required is 50-350° C., preferably 100-300°C., and more preferably 140-240° C. No catalyst is required in themethod according to the invention. The residence time in the reactionzone is from 0.1 ms to a few seconds at maximum, and is preferablybetween 0.1 and 300 ms.

[0007] Oxygen, as well as inert gases such as helium, argon, nitrogen ormixtures thereof with oxygen can be used as carrier gases.

[0008] According to the invention, ozone and NO₂ are employed at a ratioof <0.5. Ozone and NO are preferably employed at a ratio of <1.5.

[0009] In a preferred embodiment of the invention, ozone is supplied asan ozone/oxygen mixture, preferably 1-15 vol.-% ozone in oxygen, andmore preferably 5-10 vol.-% ozone in oxygen.

[0010] The method of the invention is carried out in a conventional flowreactor supplied with said gas mixture of ozone and NO₂ and/or NO andoptional carrier gas. Preferably, the method is performed in a reactoraccording to FIG. 1.

[0011] In FIG. 1:

[0012]1 Mixing chamber

[0013]2 Flow reactor

[0014]3 Heatable exterior jacket

[0015] In the mixing chamber 1, which is connected with the flow reactor2, ozone and NO₂ and/or NO, optionally with carrier gas, are mixedtogether. Preferably, this can be done at room temperature. The flowreactor is made of conventional materials stable under the pressureconditions used, and coating thereof with inert materials is notrequired. The results according to the invention are also achieved in aflow reactor made of normal standard steel. Optionally, the flow reactorcan be connected to a GC-MS analyzer and/or a gas flow cell with anFT-IR spectrometer, depending on the intended analysis of the reactiongas.

[0016] The method of the invention is universally applicable in that themethod allows for epoxidation of monoolefins having 2 to 16 carbonatoms, preferably up to 5 carbon atoms, most preferably propylene and C₄olefins, and of diolefins having 4 to 16 carbon atoms. The reactoraccording to FIG. 1 can be used with all of the above-mentioned olefins.

[0017] Thus, according to the invention, a continuous one-step method isprovided, which requires very little technical input, operates undermild reaction conditions, does not require a catalyst, and exhibits veryshort residence time in the reaction zone, i.e., high throughput. Theselectivity with respect to the epoxide produced is at least 68%, and,in addition, high conversion of at least about 50% is achieved.

[0018] With reference to the examples, the invention will be illustratedin more detail below.

EXAMPLES Example 1 Oxidation of Propylene to Form Propylene Oxide

[0019] A flow reactor 2 with a mixing chamber 0.1 according to FIG. 1 isused, the length of the flow reactor being 60 cm (reaction length: 35cm) and the inner diameter 16 mm. The flow reactor is made of quartz andis equipped with a heatable exterior jacket. Helium is used as carriergas for the olefin. In the mixing chamber, 11.5 vol.-% of ozone iscontacted with about 23 vol.-% N0₂ and 65.5 vol.-% oxygen. Each of thereactants is metered in gaseous form via mass flow control systems. Nocatalyst is used.

[0020] a) Reaction is performed at a pressure of 25 mbar and atemperature of 180° C.

[0021] b) Reaction is performed at a pressure of 10 mbar and atemperature of 140° C.

[0022] The results of Examples 1a and 1b are summarized in Table 1: Tem-Resi- pera- dence Propylene Propylene Pressure ture time percentageconversion Selectivity Example [mbar] [° C.] [s] [Vol.-%] [mole-%][mole-%] 1a 25 180 0.25 1.9 49.6 68.9 1b 10 140 0.28 4.0 52.2 81.3

[0023] It was found that, without using a catalyst and in spite of mildreaction conditions, exceedingly short residence time in the reactionzone and thus, high throughput (space-time yield) is possible with themethod according to the invention, the selectivity with respect topropylene oxide being very high.

Example 2 Oxidation of Trans-butylene to Form Cis/Trans-butylene Oxide(Mixture of Isomers)

[0024] Reactions are performed-under the same conditions as in Example1.

[0025] a) Reaction is performed at a pressure of 25 mbar and atemperature of 180° C.

[0026] b) Reaction is performed at a pressure of 25 mbar and atemperature of 230° C.

[0027] The results of Examples 2a and 2b are summarized in Table 2: Tem-pera- Resi- Butylene Butylene Pressure ture dence percentage conversionSelectivity Example [mbar] [° C.] time [s] [Vol.-%] [mole-%] [mole-%] 2a25 180 0.25 1.45 84.3 80.0 2b 25 230 0.23 1.45 53.1 96.9

[0028] The denotations in Table 2 correspond to those in Table 1.

[0029] Similarly, the results show that high conversion of the employedolefin and high throughput are achieved. The selectivity with respect tocis/trans-butylene oxide is nearly 100%.

Example 3 Oxidation of Isobutylene to Form Isobutylene Oxide

[0030] Reaction is performed under conditions as in Example 1, at apressure of 10 mbar and a temperature of 230° C. The reaction length is12 cm. The results are illustrated in Table 3. Tem- Iso- Iso- pera Resi-butylene butylene Pressure ture dence percentage conversion SelectivityExample [mbar] [° C.] time [s] [Vol.-%] [mole-%] [mole-%] 3 10 230 0.0783.5 74.9 75.2

[0031] High conversion with respect to olefin employed and highselectivity are achieved.

1. A method of producing epoxides via oxidation of olefins in ahomogeneous gas-phase reaction, characterized in that ozone and NO₂and/or NO are mixed, the resulting gas mixture is fed into a flowreactor, and the olefin is reacted therein at a pressure of 0.1-1000mbar and a temperature of 50-350° C.
 2. The method according to claim 1,characterized in that the reaction is performed at a temperature of100-300° C., preferably 140-240° C.
 3. The method according to claim 1,characterized in that the reaction is performed at a pressure of 1-500mbar, preferably 1-200 mbar.
 4. The method according to claim 1,characterized in that monoolefins having 2 to 16 carbon atoms ordiolefins having 4 to 16 carbon atoms are employed.
 5. The methodaccording to claim 1, characterized in that ozone and NO₂ and/or NO aremixed in a mixing chamber connected with the flow reactor, preferably atroom temperature.
 6. The method according to claim 1, characterized inthat ozone and NO₂ and/or NO are mixed using a carrier gas.
 7. Themethod according to claim 1, characterized in that ozone and NO₂ areemployed at a ratio smaller than 0.5.
 8. The method according to claim1, characterized in that ozone and NO are employed at a ratio smallerthan 1.5.
 9. The method according to any of claims 1-8, characterized inthat the method is carried out in a reactor comprised of a conventionalflow reactor (2) with heatable exterior jacket (3) and a mixing chamber(1) connected with the flow reactor (2), the flow reactor (2) optionallybeing connected to a GC-MS analyzer and/or a gas flow cell with an FT-IRspectrometer.